The present invention is in the area of monopropellant composition systems, for instance for spacecraft propulsion, in emergency systems for jet fighters or in emergency gasgeneration systems for submarines.
Spacecraft propulsion is defined as that needed for the orientation (attitude control) and positioning (orbit control including de-orbiting) of spacecraft after delivery into the required orbit by the launch vehicle. It is quite separate and distinct from launcher propulsion. The need for spacecraft propulsion beings with its separation from the launch vehicle and terminates at the end of its useful service life. It is usually the depletion of the spacecraft""s propellant that terminates its mission.
Typical requirements for attitude and orbit control are very low thrust (0.1 N typically), a pulsed operational mode for attitude control, a continuous operational mode for orbit control and accurate and repeatable performance and reliable leak-free operation. For de-orbiting the thrust can be higher.
The propulsion in this area is amongst others generated by so-called monopropellant thrusters, wherein a propellant is catalytically or thermally decomposed into hot gases which are then expanded through a nozzle. In the area of monopropellants hydrogen peroxide and hydrazine are presently traditionally used. They provide a specific impulse of respectively 1872 and 2266 m/s at an expansion ratio of 50, zero ambient pressure, chamber pressure of 1 MPa and at chemical equilibrium outflow conditions.
Both systems have, however, some drawbacks. Hydrogen peroxide is known for its instability and autodecomposition behaviour. Drawbacks of hydrazine are its toxicity and flammability.
These aspects of currently used monopropellants accordingly require high level, and thus costly, requirements for production, transport, storage, handling and disposal.
The same problems are encountered in emergency systems for jet fighters (emergency start-up of engine after flame-out) and submarines (emptying ballast tanks in emergency situation by generating gas).
It is one of the objects of the present invention to provide a monopropellant composition for spacecraft propulsion and the other uses described above, which obviates these drawbacks of the prior art system. It is a further object to provide a stable, clean, less toxic, and/or less flammable monopropellant composition. It is also an object to provide a monopropellant composition for spacecraft propulsion that could contribute to a relaxation of requirements and therefore to a reduction of costs and launch preparation time.
The present invention is based on the surprising finding that known solid high energy oxidisers such as hydrazinium nitroformate and ammonium dinitramide, when dissolved in water provide a liquid monopropellant system having a specific impulse that could be equal to the specific impulse of the conventional monopropellants, without having the disadvantage thereof.
The invention is accordingly directed to a solution of hydrazinium nitroformate (HNF) and/or ammonium dinitramide (AND) in water and/or a lower alkanol as monopropellant composition, especially in spacecraft propulsion. The amount of water and/or lower alkanol in the system should be such that the system is liquid, which determines the lower level of the amount of water. On the other hand there should be sufficient hydrazinium nitroformate (HNF) and/or ammonium dinitramide (AND) present in the system to provide the required impulse. Accordingly, the amount of HNF and/or ADM is from 25 to 95 wt. % of the composition. Due to the nature of spacecraft propulsion, this specific impulse of the propellant system should be as high as possible, in order to prolong the lifetime of the satellite.